The present invention relates to an impact head and a printing apparatus such as an impact printer.
A conventional impact printer includes an impact head having a magnetic circuit formed of a york and an armature. In the impact head, the armature rotates to drive a print wire, so that the print wire hits a printing surface through an ink ribbon, thereby performing a printing operation (refer to Patent Reference).    Patent Reference: Japan Patent Publication No. 2806871
FIG. 13 is a schematic perspective view showing a conventional impact head 24′ of a clapper type for one pin. FIG. 14 is a schematic side view showing the conventional impact head 24′. FIG. 15 is an enlarged perspective view showing a core 3′ of the conventional impact head 24′. In a case of a 24-pin head, the structure shown in FIG. 13 is arranged on 24 locations in a circle shape.
As shown in FIGS. 13 and 14, the core 3′ is formed of a magnetic material, and an armature york 6′ and a core york 7′ are laminated and fixed on an outer circumference of the core 3′. As shown in FIG. 15, the core 3′ further includes a protruding portion F′ for attracting an armature 1′. The armature 1′ includes a protruding portion E′ at a lower portion thereof to face the protruding portion F′ of the core 3′.
A coil 4′ is disposed around the protruding portion F′ of the core 3′, and a control unit (not shown) applies a current to the coil 4′. A wire 2′ is fixed to a distal end portion of the armature 1′ through welding and the likes. A circular portion A′ is formed at a rear end portion of the armature 1′ as a rotational pivot.
A spring plate 8′ formed of an elastic member such as a plate spring urges the armature 1′ at a rear end portion thereof. Accordingly, the circular portion A′ formed at the rear end portion of the armature 1′ is pressed against the armature york 6′ and the core york 7′ in an arrow direction b, thereby functioning as the rotational pivot of the armature 1′.
The spring plate 8′ is fixed to a side of a head cover (not shown). A groove portion D′ is formed in a guide holder 9′ for guiding the distal end portion of the armature 1′ in the left to right direction to be movable in the vertical direction. A reset spring 5′ is disposed in a hole formed in a bottom surface of the groove portion D′ of the guide holder 9′.
The reset spring 5′ is formed of an urging member such as a coil spring. When the armature 1′ is set in the groove portion D′ of the guide holder 9′, the reset spring 5′ lifts the armature 1′ toward an upper surface of the core 3′ (in a reset direction). It is configured that the armature 1 moves to impact toward a bottom surface of the core 3′ (in an impact direction) against the urging force of the reset spring 5′.
FIG. 16 is a schematic view No. 1 showing an operation of the conventional impact head 24′. FIG. 17 is a schematic view No. 2 showing the operation of the conventional impact head 24′. FIG. 16 is a view showing a reset state, and FIG. 17 is a view showing an impact state.
As shown in FIG. 16, in the reset state, the armature 1′ is pressed with the spring plate 8′ in the arrow direction b with the circular portion A′ as the rotational pivot. Further, the reset spring 5′ urges the armature 1′ in the reset direction. The spring plate 8′ has a portion C′, so that the protruding portion E′ of the armature 1′ is separated from the protruding portion F′ of the core 3′ by a distance Δx while the reset spring 5′ lifts the armature 1′ upwardly.
As shown in FIG. 17, in the impact state, the control unit (not shown) applies a current to the coil 4′ to generate a magnetic flux, so that the armature 1′ is attracted in the impact direction against the urging force of the reset spring 5′. Accordingly, the wire 2′ at the distal end portion of the armature 1′ moves in the impact direction while the circular portion A′ functions as the rotational pivot, thereby applying an impact.
FIG. 18 is a graph showing a current Ia applied to the conventional impact head 24′ and an armature force f1 thus generated. As shown in FIG. 18, the current Ia is applied to the coil 4′ at a timing (t=0), and is turned off when the wire 2′ reaches an impact point. When the current Ia is applied, the armature force f1 is generated for attracting the armature 1′ in the impact direction. An urging force Qf2 is applied to the armature 1′ in the reset direction, and a drive force Qf3 is a combinational force of the armature force f1 and the urging force Gf2.
In the reset state shown in FIG. 16, that is, before the timing (t=0), the armature 1′ is lifted with the reset spring 5′ in the reset direction through the urging force Qf2. When the current Ia is applied to the coil 4′ for the impact operation, the armature force f1 is generated to move the armature 1′ in the impact direction.
When an initial operation time T0 passes after the current Ia is applied at the timing (t=0), the armature force f1 balances with the urging force Qf2, and then the armature force f1 exceeds the urging force Qf2, thereby rotating the armature 1′ in the impact direction. When an impact time QTimp passes after the current Ia is applied at the timing (t=0), the armature 1′ reaches the impact position, thereby becoming the impact state shown in FIG. 17.
When the current Ia is turned off, the armature force f1 disappears, so that the armature 1′ returns in the reset direction with the urging force of the reset spring 5′. When a reset time QTres passes after the current Ia is turned off, the armature 1′ returns to the reset state shown in FIG. 16. The impact time QTimp and the reset time QTres represent a cycle time QTc of one pin. When the cycle time QTc becomes shorter, it is possible to perform the printing operation at a higher speed.
In order to shorten the cycle time QTc and perform the printing operation at a high speed, it is necessary to shorten both the impact time QTimp and the reset time QTres constituting the cycle time QTc.
In the conventional impact head 24′ of the clapper type described above, when the urging force Qf2 of the set spring 5′ decreases and the drive force Qf3 increases, the armature 1′ performs the impact operation in a shorter period of time. Accordingly, it is possible to decrease the initial operation time T0 and the impact time QTimp. In this case, however, the armature 1′ returns with the urging force Qf2 of the set spring 5′, thereby increasing the reset time QTres. Accordingly, it is difficult to shorten the cycle time Qtc after all.
When the urging force Qf2 of the set spring 5′ increases, on the other hand, it is possible to shorten the reset time QTres. However, the drive force Qf3 decreases, thereby increasing the initial operation time T0. As a result, the impact time QTimp increases, thereby increasing or making no change in the cycle time Qtc.
In view of the problems described above, an object of the present invention is to provide an impact head capable of solving the problems of the conventional impact head
Further objects and advantages of the invention will be apparent from the following description of the invention.